Petroleum pitch competes with coal tar pitch in many applications where the pitch is used as a carbon source and/or as a binder material. The critical properties that are evaluated when deciding what type of pitch to use include: (a) flow properties, as measured by softening point and/or viscosity, and (b) carbon yield, as measured by ASTM D 2416, Coking Value by Modified Conradson Carbon.
Historically, low viscosity products derived from coal tar have been used in the production of products for the refractory industry. These coal tar-derived products offer a source of carbon with low viscosity. The coking value of these coal tar-derived products (as measured by ASTM D 2416, Coking Value by Modified Conradson Carbon) is approximately 28 to 29 wt. %. One drawback, however, is that the coal tar derived materials have a relatively high level of regulated polynuclear aromatic hydrocarbons.
Therefore, another pitch property that is also becoming of increasing interest is the polynuclear aromatic hydrocarbon (PAH) content. The McHenry et al. U.S. Pat. No. 5,746,906 describes a coal tar pitch having a low PAH content and a method of making such pitch where a high softening point coal tar pitch (softening point of 120-175° C.) was mixed with a low softening point petroleum pitch to make a binder pitch having a softening point of 107-114° C. and a PAH content slightly above 15,000 ppm.
For example, in the manufacture of coal tar pitch, if more low boiling point materials are left in the pitch product, the resulting product has a lower softening point and a lower viscosity. In the case of petroleum pitch manufacturing, a high softening point petroleum pitch can be “cutback” with a hydrocarbon liquid material to produce a petroleum pitch having a lower softening point and a lower viscosity at a given temperature. Generally speaking, for a given softening point and given viscosity, a petroleum pitch will have a lower carbon yield than a coal tar pitch. However, despite a potentially lower carbon yield, petroleum pitch offers certain advantages over coal tar pitch. One such commercial example is a specialty pitch blend produced by Marathon Ashland Petroleum LLC known as A-500 pitch which is used by the refractory industry. This product offers a significant reduction in the amount of polycyclic aromatic hydrocarbons present as compared to coal derived tars.
In the past, many types of materials have been used to modify the flow properties of such petroleum products as pitch and asphalt. Historically, these have been petroleum based, non-oxygenated hydrocarbons such as diesel fuel or various types of fuel oils, kerosene or various cutback oils. However, the use of these solvent “cutback” materials often causes safety problems with flash point and a volatility if too much solvent is used.
Examples of viscosity modification of bituminous materials include the use of a floruoro or chlofloruoro derivative of lower alkanes, such as disclosed in Smith et al., U.S. Pat. No. 4,151,003.
Other methods include reducing the viscosity of heavy hydrocarbon oils by preheating a stream of heavy carbon hydrocarbon oil in a stream of gas, mixing under pressure, and passing the pressurized mixture through a nozzle to form fine oil droplets such that a strong shearing action is created as the heavy oil and gas are forced through an orifice, as described in Dawson et al. U.S. Pat. No. 5,096,566.
Therefore, there still is a need, however, to produce a viscosity modifier that is useful with petroleum pitches, but does not have the above described drawbacks associated with the viscosity modifiers currently in use.
In particular, there is a need for a viscosity modifier that provides improved characteristics to the pitch itself and to the pitch end product.
There is a further need for a viscosity modifier useful with pitch blends that provides improved safety features such as low volatility and low toxicity.
There is also a need to provide a replacement for coal tar-derived materials that still meet the industries' needs for a high carbon yield (i.e. high coking value) product.
Recently, the use of biodiesels, such as methyl esters of fatty acids derived from either soybean or animal fats have received some attention to augment diesel fuel supplies in the United States. Until the present invention, however, no one had thought to use oxygenated compounds, and in particular, biodiesels, both as a viscosity reduction agent and as a high carbon yield agent for pitches, and, in particular, for petroleum pitches.